Smokeless powder



aiented May 16, 1944 2,349,048 SMOKELESS rownnn Bill Harry Mackey and Paul Robert Milus, Wilmington, DeL, assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application September 4, 1940,

. Serial No. 355,308

- 4 Claims.

generally, in large diameters are frequently subject to hang fires.

The object of this invention is a novel smokeless powder which is not subject to hang fires when employed in large diameters. A further object is a novel smokeless powder which is progressive in burning, and. a method of producing the same. Another object is a smokeless powder which maintains its progressivebuming characteristics over long storage intervals. A' further object is a novel method of coating'smokeless powder. A still further object is a grain coated with a deterrent which is capable of retarding combustion and. which does not diffuse and migrate toward the center of the grain. Other objects will become apparent as the invention is described in detail hereinafter.

We have found that the foregoing objects are attained by our process which comprises coating a freshly-formed string of smokeless .powder and subsequently cutting'said coated string to form grains. The latter will thus be coated only on their outer surfaces and not on their ends or within the perforations therethrough. Any suitacrylic acid, such as the methyl, ethyl, n-propyl, n-butyl, and isobutyl esters.

These esters of methacrylic acid are tough and hard; and remain on the surfaces to which they have been applied. Likewise, the chitin compound known commercially as Daktose may be employed.

Due to the-nature of these agents, they not only are very effective in retarding combustion, but in addition they tend to render the coated powder more diificult to ignite. It is to obviate nitrocellulose of 13.2% nitrogen content, 25 parts .tion, and the like.

this disadvantage that we coat a string or strip of the green smokeless powder before the string is cut into grains of the desired length. The severing of the string to form grains thus exposes the end surfaces, which are uncoated. We have found that, by permitting these surfaces to remain uncoated, it is possible to effect ignition of the powder very readily by means of the ordinary percussion primers currently employed, even though the outer surface of the grain is coated with a material which is a very effective combustion retardant. Thus hang fires in larger diameters are eliminated. Moreover, such grains upon combustion yield a progressive burning.

It will be understood that the strip or string of smokeless powder may be coated in any con-- venient manner, for instance by subjecting it to the action of a solution containing the'coating agent, or to the coating agent in molten condi- However, we prefer to coat a string of powder by passing it through an aque= ous emulsion containing the coating agent in solution in a suitable solvent, because such procedure not only is conducive to the formation of a uniform coating on the powder string, but in addition the amount of material added as a coating may be regulated without undue difficulty. The time required for coating the'powder depends on various factors, such as the amount of coating desired, the type of coating, the temperature and concentration of the emulsion, etc., but these factors can be determined empirically for any desired conditions. After the powder has been exposed to the coating emulsion for the requisite time interval, it is removed and dried, in order that the coating may be set or fixed thereto. In case the powder string is green, that is to say, if it contains a large quantity of solvent, the coated string is dried in equipment adapted to permit the recoveryof the solvent evolved therefrom. After drying, the coated string is cut in the usual manner, to yield grains of desired length. These may be dried further and glazed according to known manner.

A smokeless powder manufactured in accordance with the present invention is illustrated in the following examples.

Example I A smokeless powder composed of 73.4 parts of nitroglycerin, 1.0 part potassium sulfate, and

0.6 part of diphenylamine was colloided by mingling these ingredients with solvents according to known procedure. The colloided mass was then 0.015 inch in diameter, said perforation extending longitudinally through the center oi said string. The resultant strings were ersed in a mixture comprising a stabilized 40% emulsion oi butyl methacrylate and water. After a preliminary drying, the coated sts were cut. into grains 0.091 inch in length. Analyses of the finished powder revealed that it was coated with approximately 6 parts of the butyl methacryiate. when this powder was compared with a powder oi the same composition hut'which had not been coated by firing in a bomb connected in a cathode ray osciilograph circuit provided with a piezoelectric gsuge for converting the mechanical impulse to on electric one, the graphs obtained showed that, when the powder charges were one-quarter consumed, the presence of the coating caused a decrease in the burning rate Since a progressive burning powder is one wherein the burning speed i retarded during the early stages but not in the latter stages of combustion, so that in effect the rate of pressure development is altered, it follows that the progressivity of burning of powders can be determined by comparing their burning speed at the same point f consumption during the early stages of the combustion of the powders. Likewise. any change in the rate of pressure developrhent occurring during storage of the powder may he ascertained by measuring the rate of pressure development at, any of the early stages of combustion. I

The stability of the ballistic performance of powders made in accordance with the present invention is illustrated by the following example.

Example 1! Two samples of powder were coated, the powder composition and granulation being identical with that set forth in Example ll. The samples were coated with "l and 6 parts of butyl methacrylate. The finished, coat-ed powders were tested as soon as made, and then were stored for 22 days at a temperature of 50 C., at which time they were again tested in order to determine any The foregoing results show that powders coated with an insoluble, non-explosive material ole laces such as butyl methacrylate exhibit very httle change in the rate of pressure development. even though they are subjected to extreme storage conditions. It is evident that the'stability of ballistic performance is completely satisfactory with powders of the type disclosed herein.

Our powder possesses the advantage that even though the powder grains are coated with a substantially non-volatile, non-explosive material, ignition thereof may be efiected readily because the entire surfaces of the grains are not coated. The ease of ignition which characterizes these powders is surprising, when viewed from the standpoint. of the nature of the preferred coating materials. Furthermore, regardless of the coating materials employed, hang fires in large diameter are eliminated.

Furthermore, our preferred powders, namely those coated with agents of high molecular weight as described in the foregoing, possess the additional advantage over conventional powders that they exhibit a stability of ballistic performonce which is vastly superior to that characterizing the double base smokeless powders currently manufactured, while simultaneously yield-' ing a burning which is truly progressive in charactor. Consequently, it follows that said powders may be employed after substantial periods of storage without danger that the powder has cc-.me "qulcke1"' and thus may cause injury because of changes in burning characteristics which have occurred during storage.

Although our invention has been described in detail, variations may be made without departing from the spirit or scope thereof. We intend, therefore, to be limited only in accordance with the iollowing claims. i

We claim:

1. A progressive-burning smokeless powder charge comprising grains of the pressed and cut type surface coated with an organic material of high molecular Weight not in itself explosive and substantially non-soluble and non-diiffusible in the organic nitrates of the nitrocellulose com- =ition.

2. The progressive-burning smokeless powder grain of claim 1 in which the organic material of high molecular weight is a methacx'ylic ester polymer.

3. The progressive-burning smokeless powder grain of claim 1 in which the organic material of high molecular weightis butyl methacrylate.

4. The progressive-burning smokeless powder grain of claim 1 in which the organic material of high molecular weight comprises a watersoluble chitin.

BILL WHY MACKEY. PAUL ROBERT MILUS. 

